1. Field of the Invention
The present invention relates to the treatment of vascular disease, and more particularly to an integral vascular filter system for use during medical procedures.
2. Discussion of Related Art
Percutaneous transluminal coronary angioplasty (PTCA), stenting and atherectomy are therapeutic medical procedures used to increase blood flow through the coronary arteries. These procedures can often be performed as alternatives to coronary bypass surgery. PTA (percutaneous transluminal angioplasty) and stenting can often be performed as alternatives to carotid endarterectomy, and femoral-popliteal bypass procedures. In PTA or PTCA procedures, the angioplasty balloon is inflated within the stenosed vessel, at the location of an occlusion, in order to shear and disrupt the wall components of the vessel to obtain an enlarged lumen. In stenting, an endoluminal prosthesis is implanted in the vessel to maintain patency following the procedure. In atherectomy, a rotating blade is used to shear plaque from the arterial wall.
One of the complications associated with all these techniques is the accidental dislodgment of plaque, thrombus or other embolic particulates generated during manipulation of the vessel, thereby causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. Such emboli may be extremely dangerous to the patient, and may result in myocardial infarction, stroke or limb ischemia. In 1995, Waksman et al. disclosed that distal embolization is common after directional atherectomy in coronary arteries and saphenous vein grafts. See Waksman et al., American Heart Journal 129(3): 430-5 (1995). This study found that distal embolization occurs in 28% (31 out of 111) of the patients undergoing atherectomy. In January 1999, Jordan, Jr. et al. disclosed that treatment of carotid stenosis using percutaneous angioplasty with stenting procedure is associated with more than eight times the rate of microemboli seen using carotid endarterectomy. See Jordan, Jr. et al. Cardiovascular Surgery 7(1): 33-8 (1999). Microemboli, as detected by transcranial Doppler monitoring in this study, have been shown to be a potential cause of stroke. The embolic materials include calcium, intimal debris, atheromatous plaque, and thrombi.
In order to initiate these procedures, one must first introduce a guidewire into the lumen of the vessel to serve as a conduit for other interventional devices, such as angioplasty balloons and stent delivery systems. This guidewire must be advanced into position past the location of the occlusion. Guidewires must be capable of traversing tortuous pathways within the body, consisting of bends, loops and branches. For this reason, guidewires need to be flexible, but they should also be sufficiently stiff to serve as a conduit for other devices. In addition, they must be xe2x80x9ctorqueablexe2x80x9d to facilitate directional changes as they are guided into position. Guidewires are well known in the art, and are typically made of stainless steel, tantalum or other suitable materials, in a variety of different designs. For example, U.S. Pat. Nos. 4,545,390 and 4,619,274 disclose guidewires in which the distal segment is tapered for greater flexibility. The tapered section may be enclosed in a wire coil, typically a platinum coil, which provides increased column strength, torqueability and radiopacity. A different design is identified in U.S. Pat. No. 5,095,915, where the distal segment is encased in a polymer sleeve with axially spaced grooves to provide bending flexibility. Another design is identified in U.S. Pat. No. 6,191,365, which discloses a multi-filament wire design.
Vascular filters are also well known in the art, especially vena cava filters, as illustrated in U.S. Pat. Nos. 4,727,873 and 4,688,553. There is also a substantial amount of medical literature describing various designs of vascular filters and reporting the results of clinical and experimental use thereof. See, for example, the article by Eichelter and Schenk, entitled xe2x80x9cProphylaxis of Pulmonary Embolism,xe2x80x9d Archives of Surgery, Vol. 97 (August, 1968). See, also, the article by Greenfield, et al, entitled xe2x80x9cA New Intracaval Filter Permitting Continued Flow and Resolution of Embolixe2x80x9d, Surgery, Vol. 73, No. 4 (1973).
Vascular filters are often used during a postoperative period, when there is a perceived risk of a patient encountering pulmonary embolism resulting from clots generated peri-operatively. Pulmonary embolism is a serious and potentially fatal condition that occurs when these clots travel to the lungs. The filter is therefore typically placed in the vena cava to catch and trap clots before they can reach the lungs.
Many of the vascular filters in the prior art are intended to be permanently placed in the venous system of the patient, so that even after the need for the filter has passed, the filter remains in place for the life of the patient. U.S. Pat. No. 3,952,747 describes a stainless steel filtering device that is permanently implanted transvenously within the inferior vena cava. This device is intended to treat recurrent pulmonary embolism. Permanent implantation is often deemed medically undesirable, but it is done because filters are implanted in patients in response to potentially life-threatening situations.
To avoid permanent implantation, it is highly desirable to provide an apparatus and method for preventing embolization associated with angioplasty, stenting or other procedures. In particular, it is desirable to provide a device which can be temporarily placed within the vascular system to collect and retrieve plaque, thrombus and other embolic particulates which have been dislodged and/or developed as a result of angioplasty, stenting or other procedures. Such a device is removed at the end of the procedure. U.S. Pat. Nos. 5,814,064 and 5,827,324 describe such a device, wherein the filter is expanded through the introduction of a fluid or a gas. U.S. Pat. No. 5,910,154 describes a filter, which expands through the use of a spring-based actuator. U.S. Pat. No. 6,053,932 describes a filter, which expands through the use of a cinch assembly. U.S. Pat. Nos. 6,179,861 and 6,001,118 describe guidewire-based filters where the filter resembles a windsock and is supported by one or more articulated support hoops.
One concern commonly encountered with all these devices is that the profile or outer diameter of the wire incorporating the filter tends to be substantially larger than the wire itself. This larger profile makes it difficult to cross the lesion or obstruction in the vessel. If the guidewire with filter cannot cross the lesion or obstruction, the procedure must be done without a filter in place. This can lead to accidental dislodgment of plaque, thrombus or other embolic particulates generated during manipulation of the vessel, thereby causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. Such emboli may be extremely dangerous to the patient, and may result in myocardial infarction, stroke or limb ischemia.
Another concern commonly encountered with all these devices is that the pores on the filter covering can become clogged with embolic particulates or clotted blood, thereby preventing perfusion of distal vessels during the procedure. The filter must then be collapsed, removed and replaced in order to continue the procedure. This complicates the procedure, and also temporarily leaves the site without a filter. One factor contributing to this problem is incremental blood flow turbulence and subsequent thrombus formation due to the angulation of the filter pores relative to the flow of blood.
The prior art makes reference to the use of alloys such as Nitinol (Nixe2x80x94Ti alloy), which have shape memory and/or superelastic characteristics, in medical devices that are designed to be inserted into a patient""s body. The shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity, and then, when heated within the body, to return to their original shape. Superelastic characteristics, on the other hand, generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient""s body, with such deformation causing the phase transformation. Once within the body lumen, the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase.
The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient""s body. See for example, U.S. Pat. No. 4,665,905 (Jervis).
Some guidewire designs have recommended the use of superelastic alloys. For example, U.S. Pat. No. 4,925,445 discloses a guidewire where the distal segment, and at least one portion of the proximal segment, are made from a superelastic alloy like Nitinol, where the transformation temperature from austensite to martensite occurs at 10xc2x0 C. or below. Also, U.S. Pat. No. 4,984,581 discloses a guidewire having a core of shape memory alloy, where the shape memory properties of the alloy provide both tip-deflection and rotational movement in response to a controlled themal stimulus.
However, the prior art has yet to disclose any guidewires, made from Nitinol or other suitable materials, incorporating vascular filters, which can be used to address the clinical problem of minimizing profile or diameter, so as to facilitate the crossing of a lesion or obstruction in the vessel. Also, the prior art has yet to disclose any vascular filters incorporating porous coverings designed to minimize incremental blood flow turbulence and subsequent thrombus formation, which can clog the filter and prevent perfusion of distal vessels.
The present invention provides for an integral vascular filter system, which can be used to address the clinical problem of minimizing profile or diameter to enable or facilitate the crossing of a lesion or obstruction in the vessel, and which overcomes many of the deficiencies associated with the prior art devices, as briefly described above. The present invention also provides for an integral vascular filter system incorporating a metallic mesh porous covering, which can be used to address the clinical problem of minimizing incremental blood flow turbulence, thrombus formation and clogged filters, and which overcomes many of the deficiencies of prior art devices, as briefly described above.
In accordance with one aspect, the present invention is directed to an integral vascular filter system comprising a guidewire, a prescribed filter shape in the distal portion of the guidewire, and a porous covering attached to the distal portion of the guidewire. The prescribed filter shape may be formed from a plurality of slots comprising at least one articulation point, in the distal portion of said guidewire. The distal portion of the guidewire has a smaller first diameter for insertion into a vessel, and a second larger diameter for expanding to substantially equal the diameter of the lumen of the vessel, and to be placed in generally sealing relationship with the lumen. The system further comprises actuating means for causing the distal portion of the guidewire to move from the smaller first diameter, to the larger second diameter and prescribed filter shape, and back.
In accordance with another aspect, the present invention is directed to an integral vascular filter system comprising a multi-filament guidewire, a prescribed filter shape in the distal portion of the guidewire, and a porous covering attached to the distal portion of the guidewire. The prescribed filter shape may be formed from the multi-filaments of the distal portion of the guidewire. The distal portion of the guidewire has a smaller first diameter for insertion into a vessel, and a second larger diameter for expanding to substantially equal the diameter of the lumen of the vessel, and to be placed in generally sealing relationship with the lumen. The system further comprises actuating means for causing the distal portion of the guidewire to move from the smaller first diameter, to the larger second diameter and prescribed filter shape, and back.
The integral vascular filter system enables or facilitates crossing lesions or obstructions in vessels. The filter is then actuated, and used to capture embolic particulates released during a medical procedure. The filter is then collapsed, and the system is removed from the patient.
In accordance with another aspect, the present invention is directed to an integral vascular filter system comprising a guidewire, a prescribed filter shape in the distal portion of the guidewire, and a metallic mesh porous covering attached to the distal portion of the guidewire. The distal portion of the guidewire has a smaller first diameter for insertion into a vessel, and a second larger diameter for expanding to substantially equal the diameter of the lumen of the vessel, and to be placed in generally sealing relationship with the lumen. The system further comprises actuating means for causing the distal portion of the guidewire to move from the smaller first diameter to the second larger diameter and prescribed filter shape, and back. The metallic mesh porous covering comprises parallelogram-shaped pores with acute and obtuse angles, which are designed to minimize incremental blood flow turbulence and subsequent thrombus formation, which can clog the filter and prevent perfusion of distal vessels.
The integral vascular filter system enables or facilitates crossing lesions or obstructions in vessels. The filter is then actuated, and used to capture embolic particulates released during a medical procedure. The metallic mesh porous covering minimizes incremental blood flow turbulence and subsequent thrombus formation, which can clog the filter and prevent perfusion of distal vessels. The filter is then collapsed, and the system is removed from the patient.
The advantage of the present invention is that the low profile or minimized diameter of the integral vascular filter system can enable or facilitate the crossing of lesions or obstructions in the vessel, which may not be crossable with other filter devices. Another advantage of the present invention is that the metallic mesh porous covering on the filter can minimize incremental blood flow turbulence and subsequent thrombus formation, thereby avoiding clogging of the filter during the procedure.